The present invention relates to a support device for positioning an optical element, in particular for positioning a lens. Furthermore, it relates to a lens barrel comprising such a support device and an optical exposure apparatus comprising such a lens barrel. The invention may be used in the context of photolithography processes for fabricating microelectronic devices, in particular semiconductor devices, or in the context of fabricating devices, such as masks or reticles, used during such photolithography processes.
Typically, the optical systems used in the context of fabricating microelectronic devices such as semiconductor devices comprise a plurality of optical elements such as lenses. Those lenses usually cooperate in an exposure process to transfer an image formed on a reticle or the like onto a substrate such as a wafer. Due to the ongoing miniaturization of semiconductor devices there is a permanent need for enhanced resolution of the optical systems used for fabricating those semiconductor devices. This need for enhanced resolution obviously pushes the need for an increased numerical aperture and increased imaging accuracy of the optical system. Furthermore, to reliably obtain high-quality semiconductor devices it is not only necessary to provide an optical system showing a high degree of imaging accuracy. It is also necessary maintain such a high degree of accuracy throughout the entire exposure process. Thus, in certain cases, there is a need for at least some kind of fine adjustment during the operation time of the optical system.
To obtain such a high degree of imaging accuracy it is known, among others, to adjust the position of at least certain ones of the optical elements with respect to other optical elements of the optical system used during the exposure process. This is done in order to compensate, over the entire system, for imaging errors inherent to the single optical elements of the system. To this end, it is known to use support devices supporting the respective optical element which allow for active positioning of the respective optical element in space.
A further problem in this context lies within the increased dimensions and, thus, the increased mass of the optical elements due to the increased numerical aperture of the optical system. On the one hand, the increased mass of the optical elements to be moved during adjustment poses dynamic problems due to the lowered resonant frequencies of the system. Furthermore, the increased mass of the optical elements to be supported leads to increased stresses within the support elements supporting the respective optical element.
Many of the known support devices use so-called serial kinematics wherein parts providing position adjustment in a first direction carry and position the parts providing position adjustment in a different, second direction. This serial arrangement, on the one hand, leads to an accumulation of the positioning errors and, thus, either more or less poor adjustment quality or increased effort to obtain satisfactory positioning accuracy. Furthermore, due to the actuators to be moved, such a serial arrangement implies a considerable mass to be moved and, thus, undesired low resonant frequencies of the support and lens system. Such a support device with serial kinematics is disclosed, for example, in U.S. Pat. No. 6,362,926 to Omura et al.
On the other hand, it known to use so-called parallel kinematics avoiding the problems associated with the above serial kinematics. With such parallel kinematics the parts providing position adjustment are arranged kinematically parallel, i.e. each of them provides for position adjustment without being dislocated in its entirety by the actuations of other parts providing position adjustment. US 2002/0163741 A1 to Shibazaki, for example, discloses a generic support device using parallel kinematics for holding an optical element of an optical exposure apparatus. In one embodiment, this support device comprises six support units arranged in the manner of a hexapod. Those support units allow for translatory positioning of the associated optical element along the coordinate axes of an orthogonal coordinate system (XYZ) as well as rotatory positioning of the associated optical element with respect to those coordinate axes. Such an arrangement allows for the maximum possible adjustability of the position of the optical element with six degrees of freedom. Anyway, it shows the disadvantage of a very complicated design with a large number of movable parts and manipulating mechanisms for moving those movable parts. Furthermore, the large number of manipulating mechanisms leads to an increased effort for controlling the manipulation and, thus, the positioning process.
In the general context of the above parallel kinematics, US 2002/0020069 A1 to Bottinelli et al. discloses a support device for positioning a body in space. In one embodiment this support device comprises three support units supporting said body. Each of said support units is mounted movably to a guide rail on a supporting structure for positioning the body by translating the respective support unit along its guide rail. Due to the kinematically serial arrangement of the drive mechanism within the kinematic chain of the positioning structure such a guide rail solution is not desirable for supporting an optical element to be used in the context of the above micro-lithography processes. This is due to the fact that such a solution is prone to not provide the necessary accuracy over the time due to effects of wear or setting. Otherwise, such a solution would require undesired additional effort for avoiding the above disadvantageous effects.
Furthermore, also in the general context of the above parallel kinematics, U.S. Pat. No. 4,976,582 to Clavel discloses a support device for positioning a movable element, such as a tool, in space using rod kinematics as support units. In one embodiment each of said support units is mounted movably to a longitudinal guide mechanism on a supporting structure for positioning the body by translating the respective support. This solution is similar to the above solution disclosed by Bottinelli et al. (US 2002/0020069 A1) and suffers form the same disadvantages. In another embodiment each of said support units is mounted movably to a rotational guide mechanism on a supporting structure for positioning the body by rotating parts of the respective support unit. Such a rotational guide solution, as well, is not desirable for supporting an optical element to be used in the context of the above micro-lithography processes. This is due to the fact that, again due to the kinematically serial arrangement of the drive mechanism within the kinematic chain of the positioning structure, such a solution is also prone to not providing the necessary accuracy over the time due to effects of wear or setting. Otherwise, such a solution as well would require undesired additional effort for avoiding the above disadvantageous effects. Furthermore, the rod kinematics themselves comprise several such rotational guides. Thus, for the reason outlined above, they are not desirable for supporting an optical element to be used in the context of the above micro-lithography processes.